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1991 W201 250D
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10 Posts
Discussion Starter · #1 ·
So I was driving my W201 and suddenly every electronic device went dark, but i managed to drive home. When I got home I checked the fuses, battery clamps/ground and the battery itself was also good. Nothing lights up or happens when I try to turn my key in the igniton. Has anyone else had this problem and what could cause this?
 

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1986/1990 W126
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20,672 Posts
So I was driving my W201 and suddenly every electronic device went dark, but i managed to drive home. When I got home I checked the fuses, battery clamps/ground and the battery itself was also good. Nothing lights up or happens when I try to turn my key in the igniton. Has anyone else had this problem and what could cause this?
Can I suggest filling out your profile for us please with vehicle details? Complete your Profile

Does the car still start? Just no lights?
 

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W124, 230E 5 speeds Manual, 1987
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595 Posts
1. Could be a bad alternator that has a goofy regulator
2. Could be a short circuit somewhere
3. Could be a ovp over volt protection relay

Recommend a good independent Benz shop to DIAGNOSE the problem
1. Could be a bad alternator that has a goofy regulator
2. Could be a short circuit somewhere
3. Could be a ovp over volt protection relay

Recommend a good independent Benz shop to DIAGNOSE the problem
If the battery is good and testing Okay than the elecrical equipment should work even without an alternator. + OP managed to drive home so i dont think he have a bad alternator. and this would affect the whole electrical system not only some electronics.
OVP is only for Engine management electronics and ABS and it Doesnt have anything to do with other electric equipment.
 

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W124, 230E 5 speeds Manual, 1987
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595 Posts
First I would suggest you double check the battery ground to chassis and to engine(it s connected somewhere at the transmission)
Second Check the Ignition Switch itself if only the equipment linked to that swith are not working.
 

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1991 W201 250D
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10 Posts
Discussion Starter · #6 ·
First I would suggest you double check the battery ground to chassis and to engine(it s connected somewhere at the transmission)
Second Check the Ignition Switch itself if only the equipment linked to that swith are not working.
I che
First I would suggest you double check the battery ground to chassis and to engine(it s connected somewhere at the transmission)
Second Check the Ignition Switch itself if only the equipment linked to that swith are not working.
I double checked the ground and it was good, I will check the ignition switch next.
 

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2002 Mercedes Benz ML 320
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318 Posts
With all due respect, I am going to make this statement, realizing that I used to Manage and wrench a “Benz”/ “Euro” repair shop and if I had a dollar for every “bad” alternator I have seen I would be extremely wealthy. That being said if you don’t have a “vat 40” diagnostic machine then your assumption that the alternator is ok is invalid. I have seen “new” alternators become “faulty”.
I would highly recommend that you locate a reputable independent “Benz” shop and pay them to diagnose the problem.

Said Benz shop will have the equipment to properly diagnose the problem. It may or may not be the alternator, it may or may not be a problem with the wiring harness.

I am guessing that you don’t have a “continuity” tester?

As with all vehicles a W201 has certain complexity issues and it is best for a professional to properly diagnose it. I am a great technician but I can’t diagnose this issue over the internet.
Good luck 👍
 

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1991 W201 250D
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10 Posts
Discussion Starter · #10 ·
Without proper diagnosis I’m still leaning towards a bad alternator. Or something in the main wiring harness.
I replaced the alternator about a month ago with a brand new one so it is unlikely
With all due respect, I am going to make this statement, realizing that I used to Manage and wrench a “Benz”/ “Euro” repair shop and if I had a dollar for every “bad” alternator I have seen I would be extremely wealthy. That being said if you don’t have a “vat 40” diagnostic machine then your assumption that the alternator is ok is invalid. I have seen “new” alternators become “faulty”.
I would highly recommend that you locate a reputable independent “Benz” shop and pay them to diagnose the problem.

Said Benz shop will have the equipment to properly diagnose the problem. It may or may not be the alternator, it may or may not be a problem with the wiring harness.

I am guessing that you don’t have a “continuity” tester?

As with all vehicles a W201 has certain complexity issues and it is best for a professional to properly diagnose it. I am a great technician but I can’t diagnose this issue over the internet.
Good luck 👍
Can I ask why would the alternator be the cause if the battery is good and has 12.6 volts? And would changing the voltage regulator help?
 

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2002 Mercedes Benz ML 320
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318 Posts
You can ask howevera normal voltage reading with a good alternator should be close to 13 volts. Therefore I recommend you locate a good reputable independent Benz shop. They need to diagnose the problem. There are many variables.
A). Could be the alternator
B). Could be a bad starter
C). Could be a bad relay
D). Could be a short in the wiring harness
E). Could be a bad ignition switch

as stated before I don’t think you have the proper equipment to diagnose the problem. I would recommend that you call a few independent Benz shops and ask them how much they charge to diagnose the problem.

Also as stated before I have seen “new alternators” be defective.
When the engine is running it should read close to 13 volts.

When you say that it doesn’t start does that mean it doesn’t crank over?
 

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1991 W201 250D
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10 Posts
Discussion Starter · #16 ·
You can ask howevera normal voltage reading with a good alternator should be close to 13 volts. Therefore I recommend you locate a good reputable independent Benz shop. They need to diagnose the problem. There are many variables.
A). Could be the alternator
B). Could be a bad starter
C). Could be a bad relay
D). Could be a short in the wiring harness
E). Could be a bad ignition switch

as stated before I don’t think you have the proper equipment to diagnose the problem. I would recommend that you call a few independent Benz shops and ask them how much they charge to diagnose the problem.

Also as stated before I have seen “new alternators” be defective.
When the engine is running it should read close to 13 volts.

When you say that it doesn’t start does that mean it doesn’t crank over?
I measured the 12.6 volts directly from the battery while it was not running and if i turn the key no lights on the dash turn on and it won't even try to spin the starter.
 

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2002 Mercedes Benz ML 320
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318 Posts
Based on the current information it could be:
A). A bad starter
B). A bad starter relay
C). Corrosion on the connections to the starter
D). Loose connections at the starter
E). Defective ignition switch

I will add the following statement:

At my current Benz shop we (myself and my master technician) do not just throw new parts on a vehicle in hopes of solving the issue we diagnose the problem first

That being said; do you have a vat 40 device?

It is a diagnostic tool
 

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1986 190E 2.3-16, 1992 190E 2.3, 2015 GL350 BTC 2020 GLS450
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2,469 Posts
If this car has an aftermarket stereo and/or an aftermarket alarm, a ground wire under the driver's side dashboard most likely got cut (or failed because of corrosion), and the whole electrical system cuts out.
 

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2011 SL550
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20 Posts
Without knowing this particular car, is it possible that the main fusible link from the battery positive to the fuse block(s) has failed? And if so, did it fail because there was a significant short, or just mechanical/age-related failure? Again, I don't know this car, but the wiring in my '91 300SL would have reacted this way to this failure - the (good) alternator would keep the car running until you got home, but once switched off there would be no way to get it started again...
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Mark Moulding
 
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